Okay this is probably a weird question, but I've been using my vacpot for the past month and a bit, using coffee ground with my Breville Ikon grinder a notch or two finer than its "drip" setting.

I'll boil the water in the lower chamber, snug the top chamber in, and once the water is fully into the top area I'll dump in my grounds and mix, wait a minute, and then take the spirit burner off and let the coffee kick back down into the globe.

In doing so, something very weird happens -- the grounds, once drained of coffee, take on the shape of a half sphere.. tall in the center of the upper chamber, and lower around the edges.

However, now that I've started using my new Vario grinder, the coffee drains and leaves a "flat" bunch of grounds instead of the half-tennis-ball look it had before.

I'm wondering - has anyone ever run into this behaviour before? Is one or the other preferable? Does it indicate anything or is it just something weird that happened?

I love how you describe the way the grounds flow.

But how does that relate to being a home barista?

-End

Cecil, baristas often do Vac pot coffee. Though this does not relate to espresso, it is an interesting coffee related observation.

I can make this happen every time in my Yama, by giving the slurry in the upper chamber a stir after removing the vac pot from the heat source. Never saw a correlation with the grinder, however.

CRCasey wrote:But how does that relate to being a home barista?

Chris Owens: Barista making siphon brew (the video is also an excellent exposure to using a siphon brewer).

My understanding is that the dome 'phenomenon' is related to the coffee grinds being suspended in the water during the drawdown rather than settled to the bottom (and floating on top in the slurry), so as John says, a dome is more related to how much and when you stir.

Andy Schecter explained it plausibly in this coffeed thread:

AndyS wrote:Yes, I think there is some logic that suggests that a domed cake will extract more evenly:

During the drawdown, there tends to be a higher flowrate down through the center than along the sides. That's because there is friction between the moving liquid and the stationary side walls, but no such friction in the center. Consequently, a drawdown with a level cake washes out the center of the cake more throughly than at the sides. A domed cake compensates for this by providing more resistance to flow in the center, evening out the flowrate and washing out the cake more uniformly.

The "ideal" amount of doming and the degree to which it makes a difference are open to experimentation, but the effect is real. Unlike some folks, however, I believe the rapid kind of stirring that produces a dome effect like that in the photo below is going too far.

Anyway, as a random-ish data point, I make vac pots fairly regularly with the Baratza Vario. I haven't had any trouble getting the dome. Finally, as a matter of putting it all in perspective, the tail end of James Hoffman's video blog, How does it look? has some interesting thoughts, as well as interesting discussion in the comments below the video.

OK, some thoughts:
1. The dome is produced by a swirl as the vacpot sucks the coffee into the lower bulb. Stirring usually causes this to occur, or enhances it. Even without a stir, it may still happen if the coffee draws down quickly, much like a "whirpool" can form over the drain in a bathtub.
2. A slight dome may promote an (very slightly) more even extraction. However, during the draw-down, the coffee will extract unevenly anyway - at the beginning of the drawdown the grinds may be underextracted, but a minute later, at the end, they may be overextracted. The difference here is not how much water is flowing through the grinds but how long the coffee has been in contact with the grinds. Not like drip brewing, where the outside of the grinds may be underextracted, and the center overextracted. More like a french press, where the amount of time is the dominant factor.

popeye wrote:However, during the draw-down, the coffee will extract unevenly anyway - at the beginning of the drawdown the grinds may be underextracted, but a minute later, at the end, they may be overextracted.

My siphon hint would be: if you have 1:00 drawdowns, you are grinding too fine, too coarse (at least, I've observed that grinding too coarse can slow the draw down, counterintuitive as that may seem), your grinder sucks (too many fines), or you need to replace your cloth (they get threadbare after many uses, and become easier to choke up). Alternately, you can get a metal mesh filter. These will get you 10 second drawdowns, but the cup is quite different (more like french press). Disclaimer: this is based on my own experience, which is limited and biased by my own interpretation. I may be wrong...

actually, i purchased a swissgold single cup brewer from sweetmarias (back when they sold them), cut off the "cup" sides, and use it as a filter. It works great. The reason i'm getting 1 minute drawdowns is that the seals on my 2 year old hario nouveau are dry-rotting and air is leaking in. I've tried to repair it with silicone tape, but that hasn't worked. And the five cup model that i have has been discontinued. I'll probably try a silicone caulk, unless anyone has a better suggestion?

Here's a pic of the single cup brewer. I cut the sides off and sanded down the remaining lip.

Don't sift your cloth-filtered brews? It's counter-intuitive, but I found sifting exacerbates choking/drawdown times with cloth, I suspect because of how it leaves SOME of the absolute tiniest fines behind, as I explained in that post—I think they flow right between the big particles and clog the cloth.